Oxidation of mononuclear aromatic hydrocarbons



Patented Jan. 30, 1934 UNITED STATES PATENT OFFICE? OXIDATION OF MONONUCLEAR AROMATIC 'HYDROCARBONS Alphons 0. Jaeger, Mount Lebanon, Pa., assignor to The Selden Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Application February 8, 1930 Serial No. 427,063

9 Claims.

10 for manufacturing expenses, it is necessary to employ temperature ranges so high that at least a portion of the raw. material is burned tocarbon dioxide and water, even when stabilized catalysts are used. On the other hand, especially in cases where raw materials are expensive or require purification or other expensive treatment, the combustion of too great a proportion results in 'a prohibitive material loss and it is not economical to use conversion temperatures which will give the highest reaction velocities. Thepractice has always been to strike a balance between the percentage of conversion and the rate of output, the exact figure depending on the relative cost of the initial material and the finished product.

I have now found that the percentage conversion obtainable in the oxidation of mononuclear aromatic hydrocarbons and their homologues and substitution products to intermediate oxidation products can be increased materially without relative reduction in the rate of conversion if the reaction is split up into a number of parts. This is most advantageously effected by the use of several converters in series, the reaction product being condensed out after each converter and the exhaust gases containing the unreacted portion of the aromatic compound being passed through the following converter. Remarkable increases in yield are obtained and 40 under the most favorable circumstances it is possible to obtain conversion efficiencies of typical mononuclear aromatic compounds to acids, for example benzol to maleic acid, of more than 50 60%, which compares with production efiiciencies at commercial practical loadings of 25-30% or less when a single converter is used.

The invention is in no sense limited to the use of any particular number of converters, the number used depending largely on the economics of the process; thus, for example, with an expensive raw material a'larger number of converters can be profitably employed than with a cheaper raw material where the capital investment for converters and labor cost is a relatively large item. A marked increase in emciency is noted when as few as two converters are used in series, but I have found that in some cases it is desirable to use at least four converters in series. The production of the first three converters is about the same, the fourth converter beginning to show considerable falling off, and, of course, with a larger number of converters each additional converter gives a proportionally smaller increase in yield. The num-- ber of converters which should be used is also to some extent dependent on the particular compound used, the more delicate the reaction the larger'the number of converters which will ordinarily be economically desirable.

While the present invention presents an important improvement over the prior processes when fresh reaction gases are used in the first converter, it is desirable in order to get maximum yield to recirculate a part of the reacted gases. This may take place by pumping a portion of the exhaust gases from the last converter in the series into the reaction gas stream entering the first converter, or, if desired, the recirculation can be for each converter in the series. Recirculation has a marked effect on the yield, but it should be noted'that. if the catalyst is loaded to such a point that the production of the reaction product is as high as the catalv t can give, recirculation does not seem to raise the yield any. This would indicate that the recirculation primarily prevent destruction of the product already formed, but does not aid in accelerating the oxidation of the aromatic compound itself. It should be understood, however, that this is not definitely proven, and it is possible that other factors may be involved, and accordingly the invention is in no sense limited to any theory of action of the recirculation. The present invention is applicable generally to the oxidation of aromatic hydrocarbons such as phenol and its homologues to maleic and fumaric acids, benzol and its homologues and compounds containing the group CH2-CH=CH-CH2 to maleic acid, and benzol and crude tar acids to maleic and fumaric acids. Heterocyclic compounds can also be oxidized by this process; for example, the vapor phase oxidation of furfural in multiple converters gives good yields of maleic acid.

The present invention is not limited to any particular type of converters, but it is advantageous to maintain uniform temperatures and therefore converters having relatively small catalyst compartments, such as, for example, tubular converters whose temperatures are controlled by baths, either boiling or non-boiling, can be eflec tively employed, although the invention is in no sense limited to their use, and other types of converters such as reaction gas cooled converters and thelike may be used.

Iron converters tend to form layers of iron oxide, which appears to act as a combustion catalyst and increases losses due to destruction of the oxidation product. It is, therefore, desirable to inactivate the converter walls coming in contact with the reaction gases, either by using special steels or other metals which do not form oxides of iron under the reaction conditions or by coating the walls with a compound of an alkali, alkaline earth, or'earth metal which forms a layer which is not a combustion catalyst. Of course, the invention is not limited to converters thus inactivated, this being merely an advantageous feature in the preferred modification..

The temperature at which the reaction takes place may be varied within considerable limits, good results being obtained in the case of bath cooled converters at bath temperatures between 350 and 450 C., and the optimum temperatures for the production of maleic acid of the highest quality from benzene being about 390 to 400 C for a bath cooled converter. It should be understood that the temperature will vary somewhat with the nature of the catalyst and that the invention is in no sense limited to the temperature ranges given above, which constitutemerely preferred ranges. When quinones are to be produced, of course, lower temperatures are in general used than when acids are to be produced, the temperatures varying, however, with the particular catalyst.

The amount of fresh air used may be varied within wide limits, for example from 3 to 20 liters per gram of aromatic compound oxidized. In general the amount of fresh air will beleast where the proportion of recirculated air is greatest, but this depends to a considerable extent on the loading and on the nature of the catalysts.

The invention is in no sense limited to the ranges given.

In most installations fresh vapors of the compound to be oxidized enter only the first converter of the series. This type of installation presents advantages from the equipment standpoint, but

the invention is not limited to such constructions cluded within the scope of the present invention,

and for some of the reactions covered by the invention they present important advantages in higher yield and smoothness of control.

The invention will be illustrated in greater detail in connection with the following specific examples, which are illustrative embodiments only.

Example 1 Four converters are arranged in series with small tubes and catalyst heights of from 20 to 30 cm., the volume of catalyst in each tube being about 135 0.0.

' catalyst consisting of aluminum vanadate which maintained at 390-400 0., the first converter being maintained at a slightly lower temperature than the others. Benzene vapors admixed with The converters are filled with.

air in a ratio of 1:20 are passed through the converters in series withoutrecirculation. Most of the conversion takes place in the first three converters, the product being condensed out between each pair, and a total yield of around 50% of maleic acid is obtained. If desired, a mixture of fresh air and exhaust gasesv may be used in each converter after the first which results in a slightly higher yield.

Example 2 Converters are set up as. described in Example 1, but instead of introducing fresh reaction gases only into the first converter, a mixture of fresh air and exhaust gases in the ratio of 1:4 is used in each converter after the first. In this manner the total percentage yield is raised to about 55%, but the amount of benzene charged per catalyst tube must be lowered. It should be noted that with this lower loading the last converter gives only a very small percentage -of the total conversion.

I Example 3 Converters are set up as in Example 2, but are filled with a base exchange catalyst such as that described in Example 28 of U. S. Patent No. 1,694,620 to'A. O. Jaeger, which catalyst is prepared as follows:' 18 parts of vanadium pentoxide treated with 10N potassium hydroxide solution to transform it into the coffee-brown potassium vanadite which is then mixed with the potassium aluminate solution. Thereupon the remaining of the vanadyl sulfate solution is added with vigorous' agitation. The final reaction product should remain strongly alkaline to litmus. The product is pressed, dried as usual under 100 C., broken into the fragments and then sprayed with 10% sulfuric acid until the so-called salt-like body is formed with the potassium vanadyl aluminum base exchange body which is diluted with infusorial earth. During the spraying the fragments should preferably be heated and stirred. The product obtained after treatment with air is an excellent catalyst for the vapor phase oxidation'of aromatic hydrocarbons or compounds, a gaseous mixture of the compounds and air in'the proportion of 1 to 20 being passed over the catalyst of 360-450 C. With this typ of catalyst the bath temperature can be maintained as high as 450 C. instead of 390-400 0., and much higher reaction velocities can be obtained. Benzene is vaporized and passed through with fresh air,

either with or without addition of exhaust gases,

and a high yield of maleic acid is obtained. Any unreacted benzene is of course separated and re-' used or recirculated with the exhaust gases.

Example 4 A converter system is arranged as described in 0 Example 2, but phenol is passed over instead of benzol. Crude tar phenols may be used for this purpose and the conversion to maleic and succinic acids is accompanied by an oxidation of the undesired impurities.

What is claimed as new is:

1. A method of oxidizing mononuclear aromatic compounds to intermediate oxidation products, which comprises vaporizing the compounds admixing them with an oxygen coniaining gas containing more than suilicient oxidation to oxidize the whole of the aromatic compound to the intermediate oxidation product and passing the mixture at reaction temperatures through a series of converters containing a catalyst favoring the oxidation of carbon atoms of the aromatic nucleus, the converted product being condensed out after leaving each converter, and uncondensed gases without addition of further oxygen-containing gas passing in series through the next converter.

2. A method according to claim 1, in which the reaction temperature is maintained between 390 and 450 C.v

3. A method of oxidizing the nucleus of mononuclear aromatic compounds to intermediate oxidation products, which comprises vaporizing the compounds, admixing them with an oxygen containing gas, and passing the mixture at reaction temperatures through at least four converters in series containing a catalyst favoring the oxidation of carbon atoms of the aromatic nucleus, the converted product being condensed out after leaving each converter and uncondensed gases passing in series through the next converter,

favoring the oxidation of the benzene nucleus,

4. A method of oxidizing ahydrocarbonof the benzene series to intermediate oxidation products, which comprises vaporizing it, admixing the vapors with an oxygen containin gas. and passing the mixture at reaction temperatures through a series of Y converters containing a catalyst and having associated with the effective component of the catalyst at least one compound of an alkali forming metal, the converted product being condensed out after leaving each converter,

and uncondensed gases passing in series through the next converter.

5. A method of producing an acid by oxidation of the nucleus of a mononuclear aromatic compound to intermediate oxidation products, which comprises vaporizing the compound, admixing it with an oxygen containing gas and passing the mixture in series through a plurality of converters containing a catalyst favoring the oxidation of the carbon atoms of the aromatic nucleus at a temperature of approximately 390-450 C., the catalyst containing associated with the effective component at least one compound of an alkali forming metal, the product being condensed out after each converter.

6. A method of oxidizing a hydrocarbon of the benzene series which comprises vaporizing it, admixing the vapors with an amount of oxygencontaining gas more than sufiicient to oxidize all of the benzene hydrocarbon to an intermediate oxidation product and passing the mixture at reaction temperatures through a series of converters containinga catalyst favoring the. oxidation of the benzene nucleus, the converted product being condensed out after leaving each converter and the uncondensed gases without admixture of fresh oxygen-containing gas being passed in series 'through the next converter.

'7. A method according to claim 6 in which at least three converters are used in series.

8. A method of producing an acid by oxidation of the nucleus of a mononuclear aromatic compound, which comprises vaporizing the com pound, it with an amount of oxygencontaining gas more than suflicient to oxidize all of the mononuclear compound to an acid and passing the mixture in series through a plurality of converters containing a catalyst favoring the oxidation of the carbon atoms of the aromatic nucleus at a temperature of approximately 390- 450" C., the product being condensed out after each converter and no fresh oxygen-containing gas being mixed with the uncondensed gases before passing through the further converters in the series.

9. A method of producing maleic acid from a hydrocarbon of the benzene series which comprises vaporizing the hydrocarbon, mixing it with an amount of oxygen-containing gas more than suflicient to oxidize all of the benzene hydrocarbon to maleic acid, passing the mixture in 'series through a plurality of converters containing a catalyst favoring the oxidation of the benzene hydrocarbon to maleic acid at a temperabefore passing through the further converters in the series.

ALPHONS O. JAEGER. 

